Overview of Respiratory Physiology

Purpose of Respiratory System

• Primary Function: To bring oxygen into the body and remove carbon dioxide.
  • Oxygen is transferred from the atmosphere to the lungs, then to the bloodstream, and finally to body tissues.
  • Carbon dioxide as a byproduct of ATP production moves from tissues to the bloodstream, to the lungs, and is then exhaled.

Atmospheric Pressure

• Sea Level: 760 mmHg of pressure exerted by gases.
• Mount Everest: Fewer gas molecules, resulting in lower pressure (e.g., ~600 mmHg).
• Dalton's Law: Total pressure of a gas mixture is the sum of individual gas partial pressures.
  • Nitrogen: 78% of atmosphere (~593 mmHg).
  • Oxygen: 21% (~160 mmHg).
  • Carbon dioxide: 0.03% (~0.3 mmHg).

Gas Laws

1. Boyle's Law: Inverse relationship between volume and pressure of a gas in a container.

   • Increase in thoracic cavity volume decreases pressure and allows air in.
   • Muscles involved include diaphragm and intercostals.

2. Henry's Law: Gas solubility in a liquid is proportional to its partial pressure.

   • Oxygen and carbon dioxide exchange across alveolar and capillary membranes.

3. Gas Exchange Phases:

   1. Ventilation: Air movement into and out of the lungs.
   2. External Respiration: Gas exchange at the respiratory membrane.
   3. Gas Transport: Movement of gases in the bloodstream.
   4. Internal Respiration: Gas exchange between blood and tissues.

Mechanics of Breathing

• Inspiration:
  • Diaphragm contracts, increasing thoracic volume and decreasing pressure.
  • External intercostals contract, expanding the rib cage.
• Expiration:
  • Diaphragm and intercostals relax, decreasing thoracic volume and increasing pressure.
  • Forced expiration involves internal intercostals and abdominal muscles.

Alveolar Function

• Gas Exchange: Oxygen decreases from 160 mmHg in the atmosphere to 104 mmHg in the alveoli.
• Carbon Dioxide: Increases from 0.3 mmHg in the atmosphere to 40 mmHg in the alveoli.
• Surfactant: Produced by type 2 alveoli cells to prevent collapse by reducing surface tension.

Clinical Application

• Emphysema: Destruction of elastic tissue due to smoking.
  • Airways collapse during forced exhalation.
  • Results in hyperinflation of lungs, requiring accessory muscle use for respiration.

Summary

• Respiratory Physiology: Understanding involves pressure gradients, muscle mechanics, and gas laws.
• Importance of Elastic Tissue: Maintains open airways and efficient breathing.

Note: This is a summarized overview based on a lecture by Dr. Mike, focusing on the mechanics and physiology of respiration.